KR101164518B1 - Monitoring Method for Crack Growth in Real Steel Structure and Estimation Method for Residual life of Real Steel Structure - Google Patents

Abstract

The present invention provides a method for monitoring crack propagation in a steel structure and a method for estimating the remaining life of the steel structure.

In the present invention, a plurality of potential difference measuring terminals are preferably arranged in a lattice shape on the surface of the steel structure to form a potential difference measurement region, and two of the plurality of potential difference measurement terminals are paired while applying current to the region. The potential difference is measured intermittently or continuously with respect to the measuring terminal pair. The full-length fingerprint coefficient FC value is calculated from the obtained potential difference. The crack propagation amount is monitored from the FC value measured in the steel structure using the master curve, using the master curve as the relationship between the crack propagation amount and the FC value determined using a test body that simulates the steel structure in advance. In addition, the same measurement terminal pairs of steel structures can be obtained from the master curve using the relationship between the load repetition frequency up to the limit repetition frequency at which the test body collapses and the FC value, which are determined using a test body that simulates the steel structure in advance. The load load repetition number corresponding to each FC value measured at the time interval t is read at, and the remaining life of the steel structure is estimated using the load repetition frequency.

Steel structure, crack propagation, remaining life

Description

Monitoring Method for Crack Growth in Real Steel Structure and Estimation Method for Residual life of Real Steel Structure}

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows an example of the arrangement | positioning of the electrode and potential difference measuring terminal which are comprised in the potential difference measuring area in this invention,

2 is a graph showing an example of an FC value-fatigue crack growth curve as a master curve for crack growth monitoring;

3 is an explanatory diagram showing a combination of an electrode set in a measurement region, a terminal for measuring potential difference, and a pair of measurement terminals;

4 is a graph showing an example of a relationship between an FC value and a load load repetition frequency;

Fig. 5 is a graph schematically showing a curve of FC value-load load repetition frequency, which is used as a master curve for remaining life estimation;

6 is an explanatory diagram schematically showing an outline of a purlin member (steel structure) used in the embodiment of the present invention.

※ Explanation of sign

11: electrode

2, 2a, 2b,... … ; 21, 22,... … : Terminal for measuring potential difference

(Patent Document 1)

Japanese Patent No. 3167449

(Non-Patent Document 1)

R. D. Strommen, H. Horn and K. R. Wold: FSM-a unique method for monitoring corrosion pitting erosion and cracking, NACE Corrosion paper no. 7, 1992

The present invention relates to a method of nondestructive testing of cracks in structures, particularly steel structures, and more particularly to a method of monitoring crack propagation and non-destructive monitoring of crack propagation and a method of estimating the remaining life of steel structures.

In steel structures, scratches, such as corrosion or cracking, are often generated in the material constituting the steel structure depending on the use environment. For example, in petroleum plants and power plants, steel structures and piping (hereinafter referred to as "devices") are exposed to a strong corrosion environment, and stress corrosion (SCC) and sulfide stresses are applied to steels constituting the devices. Corrosion (SSCC), grain boundary corrosion, etc. may occur, and thickness may decrease, and a crack, such as a crack, may arise inside or the surface by the stress acting on an apparatus etc. In addition, for example, in a steel structure to which a cyclic load acts, such as a bridge, a fatigue crack may generate | occur | produce and progress in the steel which comprises a steel structure. Scratches such as corrosion and cracks generated in such materials are often the cause of destruction of steel structures, and therefore, it is necessary to detect them early from the viewpoint of safety and safety.

As the non-destructive inspection method in which information on the size and shape of scratches such as thickness reduction and corrosion or cracking can be obtained with a relatively high accuracy, there is a potential difference method. The potentiometric method allows a current to flow through an object to be measured, measures a potential difference at a position between the scratches, and uses a calibration curve previously obtained from the result to determine the shape and dimension of the scratch included in the object to be measured. I want to get information.

For example, Patent Document 1 proposes a non-destructive inspection method for three-dimensional cracks by a direct current potential difference method. The technique described in Patent Literature 1 measures the potential difference distribution on the surface of the substrate, compares the difference between these measured values and the hypothetical potential difference distribution obtained from the assumed shape crack, and crack shape so that the difference between the measured value and the calculated value is small. By estimating the shape of the crack by changing the shape, the shape, dimensions, and inclination of the three-dimensional crack of any aspect ratio can be quantitatively evaluated. Moreover, according to the technique of patent document 1, application to the weld part which is difficult to apply an ultrasonic flaw detection method, an X-ray transmission method, etc. is made easy.

In addition, Non-Patent Document 1 introduces a FSM (Field Signature Method) for non-destructively detecting corrosion and cracks occurring in steel structures by applying a potential difference method. The FSM introduced in Non-Patent Document 1 is characterized by being capable of stably flowing a high current DC current, and is intended to detect scratches such as corrosion or cracking by using a minute potential difference between a plurality of measurement terminal pairs. .

The technique described in Patent Literature 1 is characterized by quantitatively estimating the current state of a crack from measured values measured using a potential difference measuring method for measuring a potential difference distribution between respective points set on a measurement surface. Therefore, it was impossible to estimate the direction and magnitude | size of a crack propagation by the technique of patent document 1. Moreover, even if the technique of the nonpatent literature 1 was used, it was not possible to specify the magnitude | size of a crack (dimension, shape, etc.), and to quantitatively identify the direction and magnitude of crack propagation. Above all, it was not possible to quantitatively detect and estimate the size of the crack and the amount of its growth by measuring it at the time of load load or at a vibration field.

The present invention solves such a problem of the prior art, and can easily monitor the magnitude and direction of crack propagation regardless of environmental conditions such as load load or vibration, even in the welded part or the repair part of the steel structure. To provide a method for monitoring crack propagation in steel structures, and a method for estimating the remaining life of steel structures, which can estimate the period of time until the utilization of steel structures is reached, or when repairs are required. do.

MEANS TO SOLVE THE PROBLEM In order to achieve the said subject, the present inventor first used the large test body which imitated the bridge member, and arrange | positions a some potentiometric measuring terminal on the surface of the predetermined part of the said large test body, Preferably it arrange | positions a potential difference measuring area | region. The relationship between the potential difference distribution which arises in the said potential difference measurement area | region, and the amount of growth of the crack calculated | required using the crack gauge was examined in detail. As a result, the present inventors have found that the full-length fingerprint coefficient FC value calculated from the slight change in potential difference occurring in the potential difference measurement region shows a good correlation with the amount of crack growth. And it was found that this correlation is not influenced by measurement environmental conditions such as load loading and vibration.

Further, the inventors of the present invention have described the repetition frequency (period) of the load load from the relationship between the full length fingerprint coefficient FC value and the repetition frequency of the load load to the full length fingerprint coefficient FC value and the service life (life) of the steel structure to be subjected. We found that) has a good correlation, and it was thought that by using this relationship, the remaining life of the steel structure can be estimated with high precision.

The present invention has been completed with further studies based on the above-mentioned facts. That is, the gist of the present invention is as follows.

(1) A plurality of potential difference measuring terminals are arranged in a lattice shape at predetermined intervals on the surface of the steel structure to form a potential difference measurement region, and a current is applied to the surface of the steel structure through a pair of electrodes provided with the potential difference measurement region interposed therebetween. While applying, the potential difference generated in the plurality of measurement terminal pairs is intermittently or continuously with respect to the plurality of measurement terminal pairs formed by pairing two of the plurality of potential difference measurement terminals in the potential difference measurement region. In measuring and monitoring the progress of the crack in the said potentiometric measuring region, the test body which simulated the structure previously was produced, and the test body arrange | positioned the some terminal for potentiometric measurement in the lattice form similarly to the said potentiometric measuring region. Provide an area, load a cyclic load on the specimen, Or by repeating heating and cooling, generating a crack, advancing a crack, or advancing an existing crack, and measuring the amount of growth of the crack in the tip region of the crack, while providing a pair of the pair provided with the measurement region therebetween. A plurality of pairs of measurement terminals formed by pairing two of the plurality of potential difference measuring terminals in the measurement area at the same time as measuring the amount of propagation of the crack while applying current to the surface of the test body via an electrode. For each of the plurality of measurement terminal pairs, potential differences generated in the plurality of measurement terminal pairs are respectively measured, and the full-length fingerprint coefficient FC values defined by Equation 1 below are calculated for each of the plurality of measurement terminal pairs.

(1)

FC _i (ppt) = {(A _i / B _i ) × (B _S / A _S ) -1} × 1000

Where A _i is the potential difference between the pair of measurement terminals at time i (at measurement time), B _i is the potential difference between the pair of terminal pairs at time i (at measurement time), A _{S is} time S or monitoring starts. The potential difference of the pair of measurement terminals at the time of measurement, B _S : the time difference or the measurement of the potential difference of the pair of combination terminals at the start of monitoring, and the pair of potential pairs of the pair of the combination terminals are measured in a different material from the test body. Proceed identically to the measurement of the potential difference of each pair of measuring terminals in the area)

For each pair of measurement terminals, a relationship between the amount of crack propagation and the full-length fingerprint coefficient FC value is obtained to obtain a master curve.

From the respective potential differences with respect to the plurality of measurement terminal pairs measured in the potential difference measurement region, a full-length fingerprint coefficient FC value defined by Equation 1 is calculated for each of the plurality of measurement terminal pairs, and the measurement terminal pairs A method for monitoring crack growth in steel structures, characterized by estimating the amount of crack growth in steel structures with reference to the master curve from the calculated total length fingerprint coefficients FC values.

(2) The method for monitoring crack growth according to (1), wherein the crack is a fatigue crack.

(3) The method for monitoring crack growth according to (1) or (2), wherein the current is a direct current or a direct current pulse current or an alternating current.

(4) The method for monitoring crack growth according to (3), wherein the direct current or direct current pulse current is 10 to 2000 A.

(5) The method for monitoring crack propagation according to any one of (1) to (4), wherein a potential difference Ai generated in each pair of measurement terminals is used instead of the full-length fingerprint coefficient FC value.

(6) A plurality of potential difference measuring terminals are arranged on the surface of the steel structure at predetermined intervals to form a potential difference measurement region, and a current is applied to the surface of the steel structure through a pair of electrodes provided with the potential difference measurement region therebetween. Intermittently or continuously measuring the potential difference occurring in the pair of potential difference measurement terminals with respect to at least one pair of potential difference measurement terminals formed by pairing two of the plurality of potential difference measurement terminals in the potential difference measurement region. In estimating the remaining life of the steel structure,

Prepare a test specimen that simulates the structure in advance, and provide a measurement region in which the plurality of potential difference measuring terminals are arranged in the test specimen in the same manner as the potential difference measurement region, and load or repeat the load on the test specimen to generate and propagate a crack. Alternatively, a current is applied to the surface of the test body through a pair of electrodes provided with the measurement region interposed while advancing an existing crack, so that two of the plurality of potential difference measuring terminals in the measurement region are paired. For the at least one pair of measurement terminals formed by intermittently, the potential difference occurring in the pair of measurement terminals is measured intermittently or continuously, and the full-length fingerprint coefficient FC _i value defined by Equation 1 is determined from the potential difference to the measurement terminal pair. At the same time calculating

(1)

FC _i (ppt) = {(A _i / B _i ) × (B _S / A _S ) -1} × 1000

Where A _i is the potential difference between the pair of measurement terminals at time i (at measurement time), B _i is the potential difference between the pair of terminal combinations at time i (at measurement time), A _{S is at} time S or at the start of monitoring. The potential difference of the measurement terminal pair, B _S : time S or the potential difference of the combination terminal pair at the start of monitoring and the potential difference measurement of the combination terminal pair are different from the test body in the steel material and the potential difference measurement region in the test body. Proceed the same as measuring the potential difference of each pair of measuring terminals

The load load repetition frequency at the time of measurement is recorded, and the relationship between the full-length fingerprint coefficient FC _i value and the load load repetition frequency for each pair of measurement terminals is determined, or the load load repetition number at which the test body collapses or the load load repetition immediately before it. The full length fingerprint defined by Equation (1) is obtained by using the potential difference A _i of the pair of potential difference measurement terminals measured at time i in the potential difference measurement region by _{obtaining a} limit iteration number N _cr which is the number of times. The coefficient FC _i value is calculated, and the load repetition frequency N _i corresponding to the calculated full-length fingerprint coefficient FC _i value is read from the master curve, and then time i after time interval t from time i (i + 1) Using the potential difference A _{i +1} of the pair of potential difference measurement terminals measured at, a full length fingerprint coefficient FC _{i +1} value defined by Equation 1a is calculated,

(Equation 1a)

FC _{i +1} (ppt) = {(A _{i +1} / B _{i +1} ) × (B _S / A _S ) -1} × 1000

Where A _{i +1} is the potential difference between the pair of measurement terminals at time (i + 1) (at measurement), B _{i +1} is the potential difference between the pair of combination terminals at time (i + 1) (at measurement), A _S : potential difference of measurement terminal pair at start of time S or monitoring, B _S : potential difference of combination terminal pair at start of time S or monitoring)

From the master curve, a load repetition frequency N _{i + 1} corresponding to the calculated full-length fingerprint coefficient FC _{i + 1} value is read, and the remaining service life L of the steel structure is estimated by the following equation (2). Remaining life estimation method.

(Equation 2)

L = {t × (N _cr -N _{i +1} ) / (N _{i +1} -N _i )}

Where L is the remaining life of the steel structure, t is the interval from time i to time (i + 1), N _{cr is the} limit number of iterations, and N _{i is} the FC value measured on the steel structure at time i on the master curve. Load load repetition number read, N _{i + 1} : Load load repetition number read on master curve from FC value measured in steel structure at time (i + 1)

(7) The residual in the steel structure according to (6), wherein the potential difference A _i and A _{i + 1} generated in each pair of measurement terminals is used instead of the full-length fingerprint coefficient FC _i value and FC _{i + 1} value. Life Estimation Method.

(8) The method according to (6) or (7), wherein the potential difference measurement region and the measurement region are regions in which a plurality of potential difference measurement terminals are arranged in a lattice shape.

(9) The method of estimating the remaining life in a steel structure according to any one of (6) to (8), wherein the current is a direct current or a direct current pulse current or an alternating current.

(10) The method for estimating the remaining life of a steel structure according to (9), wherein the direct current or direct current pulse current is 10 to 2000 A.

Best Mode of the Invention

The present invention is directed to steel structures, and particularly to welded steel structures in which cracking and propagation are likely to occur frequently, and the safety of structures is strictly required. Incidentally, the cracks mentioned herein include cracks such as cracks caused by fatigue or thermal stress, cracks caused by stress corrosion, and the like.

In the present invention, a potential difference measuring region M is formed on the surface of a steel structure (hereinafter also referred to as a steel structure) in which crack generation and development are expected. There is no problem even if the potential difference measuring region M is set in plural parts. In the potential difference measuring region M, the plurality of potential difference measuring terminals 21, 22,... Are spaced at predetermined intervals, and are preferably arranged in a lattice shape. It is also preferable to arrange one side of the grating in a direction perpendicular to the main stress.

An example of the potential difference measuring region is shown in FIG. 1. In FIG. 1, twelve potential difference measuring terminals are arranged, but of course, the present invention is not limited thereto.

In the vicinity of the outer edge of the potential difference measurement region M, it is preferable to arrange the pair of electrodes 11 and 11 at arbitrary positions with the potential difference measurement region M therebetween. The pair of electrodes 11 and 11 are wired with a current supply wire (not shown), so that a current can be applied from the power supply (not shown) to the surface of the steel structure to be measured. The electrodes to be arranged are not limited to one pair, and there is no problem even if a plurality of pairs of electrodes having changed directions are arranged. In the present invention, the current to be applied is preferably a direct current, and in particular, a direct current pulse current. In addition, when detecting the micro crack in the outer surface, you may make it alternating current. The value of the current to be applied is not particularly limited as long as it is possible to measure the potential difference between the terminals for measuring the potential difference, but the value of 10 to 600 A can correspond to a wide range of thicknesses from thin to thick. desirable.

The measurement ends of the potential difference measuring means (not shown) are connected to the plurality of potential difference measuring terminals (hereinafter also referred to as measurement terminals) 21, 22, ... through a potential difference measuring lead. The kind of the potential difference measuring means is not particularly limited as long as it can be connected between a pair of terminals for measuring the potential difference (hereinafter also referred to as a measurement terminal pair), and the potential difference between these pairs of measurement terminals can be measured. After the potential difference measurement between a pair of potential difference measurement terminals is complete | finished, the terminal connected next is switched and the potential difference of another pair of measurement terminals is measured. It is preferable that the switching of the measurement end of the potential difference measuring means is automatically switched in a manual or pre-programmed order by a switching means (not shown) such as a switching switch.

In the measurement of the potential difference, it is preferable to provide a plurality of terminals as combination terminal pairs in steel materials other than the target steel structure in order to eliminate a change in resistance caused by a cause other than crack generation and propagation, such as temperature change of the steel structure to be measured. Do.

While applying current between the electrodes provided on the surface of the steel structure to be measured, by means of the potentiometric measuring means, between each pair of measuring terminals, preferably arranged in a lattice shape, for example, between 2a-2b in FIG. The potential difference between 2b-2c, 2c-2d, 2e-2f and the like is measured. In addition, in the potential difference measurement of the measurement terminal pair in the potential difference measurement region, it is preferable to simultaneously measure the potential difference of the combination terminal pair. Such measurement of the potential difference for each pair of measurement terminals is performed intermittently or continuously at desired time intervals.

First, the monitoring method of the crack propagation in a structure is demonstrated.

In the present invention, as an index of crack propagation, using the full-length fingerprint coefficient FC _i defined by Equation 1 below,

(1)

FC _i = {(A _i / B _i ) × (B _S / A _S ) -1} × 1000

Where A _i is the potential difference between the pair of measuring terminals at time i

B _i : Potential difference of the pair of terminals for combination at time i (at measurement)

A _S : Potential difference between pairs of measurement terminals at time S (measurement start) or monitoring start

B _S : Potential difference between the pair of terminal pairs at time S (measurement start) or monitoring start)

The full-length fingerprint coefficient FC _i is calculated for each pair of measurement terminals from the potential difference A _i measured for each pair of measurement terminals. In addition, when the steel structure to be used has a small change in temperature, applied current, and the like, there is no problem even if the potential difference A _i , which is a measured value, is used as it is instead of the full-length fingerprint coefficient FC _i value.

In the monitoring of crack propagation in the steel structure according to the present invention, the measurement is performed at each measurement time from a master curve previously obtained using the full-length fingerprint coefficient FC _i in each measurement terminal pair of each measurement time obtained as described above. Estimate the amount of crack propagation.

The master curve in the crack growth monitoring method in the steel structure is determined in advance as follows.

A test specimen simulating the steel structure is made of the same kind of steel as the steel structure under test. The test body is preferably provided with a measurement region in which a plurality of potential difference measuring terminals are arranged in a lattice shape. In this test body, crack propagation amount measuring means is provided in a region where cracks are generated and growth is expected. As the crack propagation amount measuring means, distortion gauges such as crack gauges, ultrasonic waves, X-rays, and the like are preferable, and the crack propagation amount measuring means as described above is provided in the region where cracks are generated and growth is expected. For example, in the case of a crack gauge, a crack gauge etc. are attached. In addition, the crack gauge used suitably by this invention can apply all commercially available things, The kind is not specifically limited. The crack propagation measuring unit may be measured by a ruler or eye as long as the accuracy does not matter.

The test specimen is loaded with a cyclic load to generate and propagate a crack, or to propagate an existing crack, and the amount of crack propagation is measured at the tip region of the crack by means of a crack propagation measurement means such as a crack gauge. . In the present invention, the current is applied to the surface of the specimen through a pair of electrodes provided with the measurement region of the test body therebetween, and at the same time as the measurement of the amount of growth of the crack, two of the plurality of potential difference measuring terminals in the measurement region of the test body are measured. For a plurality of pairs of measurement terminals formed by pairing dogs, the potential difference generated in each pair of measurement terminals is measured. At the same time as measuring the potential difference in the pair of measuring terminals, measuring the potential difference of the pair of pairs of terminals provided in a steel material different from the test body is the same as the measurement of the potential difference of each pair of measuring terminals in the potentiometric measuring region. In addition, you may repeat heating cooling instead of a repeat load. In addition, of course, in this invention, if a crack generate | occur | produces and advances, it is not limited to these.

The potential difference A _i occurring at the measurement terminal pair in the measurement region of the test body measured at a certain time i, the potential difference B _i of the combination terminal pair at that time, and the measurement terminal pair at the start of the measurement (starting the monitoring) and a potential difference occurs in the _S a, _S B by the use of a potential difference of the combined pair of terminals for a time, and calculates the electric field fingerprint coefficient FC _i to be defined by the equation (1). This is done for each pair of measurement terminals in the measurement region of the test body.

Then, for each pair of measurement terminals in the measurement region of the test body, the crack growth amount obtained as described above and the full-length fingerprint coefficient FC _i at that time are related to each other and the relationship between the crack growth amount and the full-length fingerprint coefficient FC value is also shown. Create an FC value-crack propagation curve.

For example, when the measurement area is set as shown in FIG. 3 and fatigue cracks are generated and developed, for example, a curve (relationship between fatigue crack growth amount and FC value) as shown in FIG. 2 is applied to each pair of measurement terminals. Obtained. 2 is a case where it measured in the static load: 0 kN state. As shown in Fig. 3, the fatigue crack is generated between the measurement terminals 22 and 23 (measurement terminal pair No. 2), and the measurement terminal pair no. Advancing between the two. FC value is measured terminal pair No. 2 (between 22 and 23), measuring terminal pair No. From 5 (between 26 and 27) to the + (plus) side, measure terminal pair no. 1 (between 21 and 22), measuring terminal pair No. It ranges from 3 (between 22 and 23) to-(minus).

It can be seen from FIG. 2 that the FC value and the crack growth amount have a good correlation. Therefore, the crack propagation amount can be estimated from the measured FC value using the FC value-crack propagation curve as shown in FIG. 2.

In the present invention, the FC value-crack propagation amount curve as shown in Fig. 2 is previously determined in the same order as described above using a test specimen, and is used as a master curve for crack propagation monitoring. In addition, crack growth is of course not limited to fatigue cracking. In the present invention, the crack growth amount in the steel structure is monitored by using the FC value measured in the steel structure to determine the amount of crack growth from the predetermined crack growth monitoring master curve.

According to the studies by the present inventors, the FC value in the relationship between the fatigue crack growth amount and the FC value shown in FIG. 2 serving as the master curve hardly changes even if the load to be loaded changes. It is also confirmed that the FC value of the measuring terminal pair in which the crack is present or the measuring terminal pair in the crack propagation direction is almost unchanged even under vibration. In addition, the FC value of the pair of measuring terminals in the position where the crack does not exist or is out of the propagation direction of the crack is disturbed due to the vibration of the current. In other words, it was confirmed that in the crack propagation direction region, the monitoring can be performed with good accuracy because it is hardly influenced by the monitoring environmental conditions such as load load and vibration under the live load environment. In addition, the present inventors have confirmed that the FC value-crack propagation amount curve as shown in FIG. 2 becomes constant irrespective of the measurement portion of the base material portion, the weld portion, the repair portion, and the like of the steel structure. This is a breakthrough in its application to steel structures.

Next, the remaining life estimation method in the steel structure of the present invention will be described.

On the surface of the steel structure to be subjected to the residual life estimation, a plurality of potential difference measuring terminals are spaced apart at predetermined intervals to form a potential difference measurement region. And applying a current to the surface of the steel structure via a pair of electrodes provided with the potential difference measuring region interposed therebetween, and forming a pair of two of the plurality of potential difference measuring terminals in the potential difference measuring region. For at least one pair of potential difference measuring terminals, the potential difference occurring in the pair of potential difference measuring terminals is measured intermittently or continuously at a desired time interval. The full-length fingerprint coefficient FC value of each pair of potential difference measurement terminals at each measurement time is calculated using the above equation 1 from the measured potential difference. This is the same as the method for monitoring crack propagation in the above-described steel structure.

In the residual life estimation of the steel structure according to the present invention, the remaining life estimation obtained in advance using the full-length fingerprint coefficient FC value of each measurement terminal pair at each measurement time measured in the steel structure as described above. The corresponding load load repetition frequency is read from the dragon's master curve to estimate the remaining life of the steel structure as a target.

First, the determination method of the master curve for remaining lifetime estimation is demonstrated.

The test specimens simulating the steel structure are made of the same kind of steel as the steel structure. The test body is provided with a measurement region in which a plurality of potential difference measurement terminals are arranged in a lattice shape, preferably at the same position as the potential difference measurement region disposed in the steel structure. Then, the specimen is loaded with a cyclic load, and cracks are generated and developed, or existing cracks are developed, and a current is applied to the surface of the specimen through a pair of electrodes provided with the measurement region of the specimen therebetween to measure the specimen. For a plurality of pairs of measurement terminals formed by pairing two of the plurality of potential difference measuring terminals in the region, the potential difference generated in each pair of measurement terminals is measured intermittently or continuously. In addition, the number of load load repetitions is recorded simultaneously with the measurement of the potential difference in the pair of measuring terminals. At this time, the measurement of the potential difference of the pair of combination terminals provided on the steel material different from the test body is the same as the measurement of the potential difference of each pair of measurement terminals in the potential difference measuring region.

And from the potential difference which arises in each pair of measuring terminals obtained from the test body, the full-length fingerprint coefficient FC value defined by the said Formula (1) is computed for every pair of measuring terminals of a test body, and for each pair of measuring terminals in a test body, it is shown in FIG. The full-length fingerprint coefficient FC value-load load repetition curve, which is a relationship between the full-length fingerprint coefficient FC value and the load load repetition frequency as shown, is obtained. The relationship between the full-length fingerprint coefficient FC value and the load load repetition frequency for each pair of measuring terminals in the test specimen is determined to the limit repetition frequency N _cr which is the load load repetition number at which the test object collapses or the load load repetition number immediately before the test body. The total fingerprint coefficient FC value-load load repetition frequency curve is obtained until n × N _cr multiplied by the safety factor n. In the present invention, the full-length fingerprint coefficient FC value-load load repetition curve up to the limit repetition number N _cr or n × N _cr obtained in this way is used as the master curve for remaining life estimation. In the present invention, the full-length fingerprint coefficient FC value-load load iteration curve as shown in Fig. 4 is used as the master curve. In addition to the change in the full-length fingerprint coefficient FC value due to the presence of cracks in the master curve, the change in the full-length fingerprint coefficient FC value also includes the damage of the structure itself. This means that it is possible to estimate the remaining life of.

Using the master curve obtained in the above order, a method for estimating the remaining life of the steel structure will be described in detail. An example of a master curve is shown typically in FIG.

First, the potential difference generated for each pair of potential difference measurement terminals formed by pairing two of the plurality of potential difference measurement terminals in the potential difference measurement region provided in the target steel structure is measured at a desired time interval. Using the potential difference A _i generated in the pair of potential difference measurement terminals measured at an arbitrary time i, the full-length fingerprint coefficient FC _i value defined by the above expression (1) is calculated. In addition, when the steel structure to be used has a small temperature change, a current change, etc., there is no problem even if the potential difference A _i , which is a measured value, is used as it is instead of the full-length fingerprint coefficient FC _i value.

4 and 5, the load repetition frequency N _i corresponding to the calculated full-length fingerprint coefficient FC value FC _i is read out from the master curve. Then, using the potential difference A _{i + 1} measured at the same potential difference measuring terminal pair at time (i + 1) after the time interval t from time i, the full-length fingerprint coefficient FC _{i +1} value defined by Equation 1a is obtained. Calculate.

(Equation 1a)

FC _{i +1} (ppt) = {(A _{i +1} / B _{i +1} ) × (B _S / A _S ) -1} × 1000

Where A _{i +1} is the potential difference between the pair of measurement terminals at time (i + 1) (at measurement), B _{i +1} is the potential difference between the pair of combination terminals at time (i + 1) (at measurement), A _S : potential difference of measurement terminal pair at start of time S or monitoring, B _S : potential difference of combination terminal pair at start of time S or monitoring)

4 and 5, the load repetition number N _{i + 1} corresponding to the calculated full-length fingerprint coefficient FC _{i + 1} value is read from the master curve. The remaining life L of the steel structure is estimated by the following equation 2 using the load repetition number N _i , N _{i + 1} read from these master curves.

(Equation 2)

L = {t × (N _cr -N _{i +1} ) / (N _{i +1} -N _i )}

Where L is the remaining life of the steel structure, t is the time interval from time i to time (i + 1), N _{cr is the} limit number of repetitions, N _i is the master value from the FC _i value measured in the steel structure at time i Number of load load repetitions read on the curve, N _{i + 1} : Number of load load repetitions read on the master curve from the FC _{i + 1} value measured on the steel structure at time (i + 1)

In addition, in this invention, the time interval t of the potential difference measurement of a steel structure is not specifically limited, What is necessary is just to repeat a potential difference measurement at least twice at desired intervals, such as time, days, and years.

Hereinafter, the present invention will be further described based on Examples.

(Example)

A new purlin member having a crack in the U-rib corner shown in Fig. 6, which simulates the steel structure, was fabricated, and crack growth was monitored while the cyclic load was loaded to estimate the crack growth amount.

On the surface of the purlin member, a monitoring region M in which a plurality of potential difference measuring terminals (2a to 21: 12 total) were arranged in a lattice shape as shown in Fig. 1 was formed. The space | interval between each contact was 30 mm. Moreover, in order to apply an electric current to this monitoring area | region M, the pair of electrodes 11 and 11 were provided around the edge part of the monitoring area | region M. As shown in FIG. In addition, the lattice of the terminal for measuring potential difference comprised in the monitoring area M was set so that one side 2a-2b and 2b-2c may be a direction orthogonal to the direction to which fatigue crack growth is anticipated. The current direction was a direction parallel to one side (2a-2b, 2b-2c) of the lattice of the terminal for measuring the potential difference.

DC pulse (pulse height: 120A, pulse time: 1.7s) was applied between the pair of electrodes 11 and 11. Using a DC potentiometer as a potentiometer, a pair of a plurality of measuring terminals were paired to form a pair of measurement terminals, and the potential difference between each pair of measurement terminals (No. A to No. I) was measured intermittently. Measuring terminal pair no. A is 2a-2b, No. B is 2b-2c, No. C is 2c-2d, No. D is 2e-2f, No. E is 2f-2g, No. F is 2g-2h, No. G is 2i-2j, No. H is 2j-2k, No. I was 2k-2l. In addition, the measurement lead wire is provided in advance in each measuring terminal, and it is a matter of course that it is set so that switching is possible by a switching switch. Moreover, in order to eliminate the change of the potential difference by a factor other than a crack, the measurement terminal for combination was provided in the steel plate different from a purlin member, and the potential difference of a pair of combination terminals was also measured simultaneously.

Using the measured potential difference A _i of each pair of measurement terminals, the full-length fingerprint coefficient FC _i defined by the above equation (1) was calculated on the basis of the start of monitoring (time S).

For the purlin member to be monitored, the FC _i value calculated using the potential difference measured on the third day from the start of measurement, and the master curve for crack propagation monitoring shown in FIG. 2 previously determined using a test body (FC value-cracking). The amount of crack growth from the start of the measurement to the third day was estimated using the amount of curve of the curve), and the amount of crack growth was 0.5 mm. The amount of crack growth from the start of measurement to the third day obtained by the crack gauge attached to the crack tip was 0.5 mm. Thus, according to the monitoring method of the crack propagation of this invention, it confirmed that the crack propagation amount can be estimated with favorable precision.

In addition, the residuals shown in Fig. 4 previously determined using a test body using the FC values calculated using the above equations (1) and (1a) from the potential difference measured at the start of the measurement and on the third day from the measurement start. The load load repetition number N was read from the master curve for life estimation (FC value-load load repetition curve), and the remaining life under the repeated load of the purlin member was estimated using Equation 2 above, and the remaining life was 38.5 days. (41.5 days from the start of measurement). On the other hand, the purlin member was destroyed at 43 days from the start of measurement. As described above, according to the method for estimating the remaining life of the present invention, it was confirmed that the remaining life of the steel structure can be predicted with good precision.

According to the present invention, it is possible to continuously monitor the crack propagation in a steel structure for a long time even in an environment that is inaccessible to humans, thereby ensuring the safety of the steel structure and at the same time remaining the life of the steel structure. Can be estimated with high accuracy, and planning such as repair and repair is easy, and the industrial remarkable effect is exhibited. Moreover, according to this invention, there exists an effect that it can monitor the progress of the crack in a steel structure easily and accurately similarly to a base material part also in welding parts, repair parts, etc. other than a base material part.

Claims (10)

A plurality of potential difference measuring terminals are arranged in a lattice shape at predetermined intervals on the surface of the steel structure to form a potential difference measuring region, and a current is applied to the surface of the steel structure through a pair of electrodes provided with the potential difference measuring region interposed therebetween. For a plurality of measurement terminal pairs formed by pairing two of the plurality of potential difference measurement terminals in the potential difference measurement region, the potential difference generated in the plurality of measurement terminal pairs is measured intermittently or continuously, respectively. In the method for monitoring the progress of the crack in the potential difference measuring region, A test specimen simulating a structure was prepared in advance, and a measurement region in which a plurality of potential difference measurement terminals were arranged in a lattice like the potential difference measurement region in the test body was provided, and the test body was repeatedly loaded with load or repeated heating and cooling. By generating or advancing a crack or advancing an existing crack, and measuring the amount of growth of the crack in the tip region of the crack, and through the pair of electrodes provided with the measurement region therebetween. The plurality of measurement terminal pairs are formed with a pair of two of the plurality of potential difference measuring terminals in the measurement area as a pair while simultaneously measuring the amount of growth of the crack while applying a current to the surface. The potential difference occurring in the pair of measurement terminals is measured, respectively, and is defined by Equation 1 below from the potential difference. Calculating an electric field fingerprint coefficient FC and each of the values to a plurality of measurement terminal pair, and each of the respective measurement terminal pair is obtained the relationship between the amount Gin of the cracking and the electric fingerprint coefficient FC values, and this as a master curve, From the respective potential differences with respect to the plurality of measurement terminal pairs measured in the potential difference measurement region, a full-length fingerprint coefficient FC value defined by Equation 1 is calculated for each of the plurality of measurement terminal pairs, and the measurement terminal pairs A method for monitoring crack growth in steel structures, characterized by estimating the amount of crack growth in steel structures with reference to the master curve from the calculated total length fingerprint coefficients FC values. (1) FC _i (ppt) = {(A _i / B _i ) × (B _S / A _S ) -1} × 1000 Where A _i is the potential difference between the pair of measuring terminals at time i (measurement time). B _i : Potential difference between pairs of terminals at time i (measurement time) A _S : Potential difference between pairs of measurement terminals at time S or monitoring start B _S : Potential difference between the pair of terminal pairs at time S or start of monitoring In the above, the potential difference measurement of the pair of combination terminals proceeds in the same way as the potential difference measurement of each pair of measurement terminals in the potential difference measurement region in the test body in a steel different from the test body. The method of claim 1, The crack growth monitoring method, characterized in that the crack is fatigue cracking. 3. The method according to claim 1 or 2, And the current is a direct current or a direct current pulse current or alternating current. The method of claim 3, wherein The DC or DC pulse current is 10 ~ 2000A, the crack growth monitoring method. delete A plurality of potential difference measuring terminals are arranged on the surface of the steel structure at predetermined intervals to form a potential difference measurement region, and the electric potential difference is applied to the surface of the steel structure through a pair of electrodes provided with the potential difference measurement region therebetween. The potential difference generated in the pair of potential difference measurement terminals is measured intermittently or continuously with respect to at least one pair of potential difference measurement terminals formed by pairing two of the plurality of potential difference measurement terminals in the measurement region. In estimating the remaining life of steel structures, Prepare a test specimen that simulates the structure in advance, provide a measurement region in which the plurality of potential difference measuring terminals are arranged in the test specimen in the same manner as the potential difference measurement region, and load and repeat the cracks by repeating the load on the specimen. Alternatively, a current is applied to the surface of the test body through a pair of electrodes provided with the measurement region interposed while advancing an existing crack, so that two of the plurality of potential difference measuring terminals in the measurement region are paired. For at least one pair of measurement terminals formed by intermittently, the potential difference occurring in the pair of measurement terminals is measured intermittently or continuously, and the full-length fingerprint coefficient FC value defined by Equation 1 is calculated from the potential difference for the pair of measurement terminals. At the same time, The load load repetition frequency at the time of measurement is recorded, and the relationship between the full-length fingerprint coefficient FC value and the load load repetition frequency for each pair of measurement terminals is measured, or the load load repetition number immediately before the test body collapses or the load load repetition number immediately before that. To the limit iteration number N _cr , which is the master curve, Using the potential difference A _i of the pair of potential difference measurement terminals measured at time i in the potential difference measurement region, a full length fingerprint coefficient FC _i value defined by Equation 1 is calculated, and the calculated full length is calculated from the master curve. The load repetition number N _i corresponding to the fingerprint coefficient FC _i value is read out, and then using the potential difference A _{i + 1} of the pair of potential difference measuring terminals measured at time i + 1 after time interval t from time _i. By calculating the full-length fingerprint coefficient FC _{i + 1} value defined by the following equation 1a, From the master curve, a load repetition frequency N _{i + 1} corresponding to the calculated full-length fingerprint coefficient FC _{i + 1} value is read, and the remaining service life L of the steel structure is estimated by the following equation (2). Remaining life estimation method. (1) FC _i (ppt) = {(A _i / B _i ) × (B _S / A _S ) -1} × 1000 Where A _i is the potential difference between the pair of measuring terminals at time i (measurement time). B _i : Potential difference between pairs of terminals at time i (measurement time) A _S : Potential difference between pairs of measurement terminals at time S or monitoring start B _S : Potential difference between the pair of terminal pairs at time S or start of monitoring In the above, the potential difference measurement of the pair of combination terminals proceeds in the same way as the potential difference measurement of each pair of measurement terminals in the potential difference measurement region in the test body in a steel different from the test body. (Equation 1a) FC _{i + 1} (ppt) = {(A _{i + 1} / B _{i + 1} ) × (B _S / A _S ) -1} × 1000 Where A _{i + 1} : potential difference between the pair of measuring terminals at time (i + 1) (at measurement) B _{i + 1} : Potential difference between pair of terminals at time (i + 1) (at measurement) A _S : Potential difference between pairs of measurement terminals at time S or monitoring start B _S : Potential difference between the pair of terminal pairs at time S or start of monitoring (Equation 2) L = {t × (N _cr -N _{i + 1} ) / (N _{i + 1} -N _i )} Where L is the remaining life of the steel structure         t: the interval from time i to time (i + 1) N _cr : limit repeat count N _i : Number of load load repetitions read on the master curve from the FC value measured in the steel structure at time i N _{i + 1} : Number of load load repetitions read on the master curve from the FC value measured in the steel structure at time (i + 1) delete The method of claim 6, The potential difference measuring region and the measuring region are regions in which a plurality of potential difference measuring terminals are arranged in a lattice shape, and the remaining life estimation method in a steel structure. The method of claim 6 or 8, Residual life estimation method for a steel structure, characterized in that the current is a direct current or direct current pulse current or alternating current. The method of claim 9, The DC or DC pulse current is 10 ~ 2000A, the remaining life estimation method for a steel structure.

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